Smokers were a big help in two studies in the Jan. 28 issue of Circulation: Journal of the American Heart Association. Both studies looked at the damage smokers inflict on their blood vessels. This damage is remarkably like that seen in the early stages of hardening of the arteries.

"When blood vessels are exposed to cigarette smoke it causes the vessels to behave like a rigid pipe rather than a flexible tube," David J. Bouchier-Hayes, MD, leader of one of the studies, says in a news release. "Thus the vessels can't [expand] in response to increased blood flow."

Earlier studies suggested that an amino acid called taurine and vitamin C each have protective effects on the tissues that line blood vessels. So the researchers repeated their tests after giving the study participants a dose of taurine, and repeated them again using vitamin C. Both nutrients -- especially taurine -- allowed the smokers' blood vessels to expand to near-normal widths.

Taurine is commonly found in many foods. It is particularly abundant in fish -- just about any kind of fish, including mild white fish. The finding, the researchers suggest, may explain why people who eat small amounts of fish each day have fewer deaths from heart disease.

In the second study, researchers led by William G. Haynes, MD, University of Iowa, Iowa City, performed a similar experiment. They looked at 14 heavy smokers aged 18 to 85, and compared them with age-matched nonsmokers. Using different methods than the Irish researchers, Haynes got similar results: The smokers' blood vessels didn't expand very much in response to increased blood flow.

That changed when the smokers got a dose of allopurinol, a drug used to treat gout. The finding, Haynes and colleagues suggest, helps scientists understand what happens to blood vessels in the earliest stages of heart disease.